1. Field of the Invention
The present invention relates to a condenser for condensing a gaseous refrigerant by cooling it, and is suitably used in a refrigerating circuit for an air conditioning system for an automobile.
2. Description of Related Art
While heating a cabin of an automobile, recent air pollution legislation makes it usual to use an inner recirculation mode, where the air in the cabin is recirculated. Heating by an inner air recirculation mode, however, may cause windows (wind shield, rear window and side windows) to be fogged. In order to prevent the windows from being fogged, an air conditioning system is, even in the winter season, operated in a dehumidifying mode so that the air in the cabin is dehumidified.
However, operation of the refrigerating system during the winter season causes the condensing pressure as well as the evaporating pressure to be reduced since the load is very small. A reduction in the pressure of the refrigerant also reduces the temperature. Namely, the temperature of the refrigerant at the evaporator can fall below 0.degree. C., which causes the evaporator to frost up. In order to prevent the evaporator from frosting up, the usual solution is to stop the compressor in the refrigerating cycle when the evaporating pressure is reduced to a predetermined value. In place of the selective stopping of the compressor, Japanese Un-Examined Patent Publication No. 63-302257 discloses a refrigerating circuit including a evaporating pressure regulator for controlling the flow amount of the refrigerant in accordance with the pressure at the evaporator for preventing the stopping of the compressor while maintaining a desired pressure in the refrigerant.
However, such a control of the evaporating pressure causes the pressure difference of the evaporator with respect to the condenser to be also reduced, which causes the amount of the refrigerant passing through an expansion valve, which is arranged between the condenser and the evaporator to be reduced. Such a reduction of the amount of the refrigerant passing through the expansion valve causes the dehumidifying capacity to be reduced at the evaporator. As a result, the effect of clearing the fog on the windows becomes insufficient.